Increasing SAT-Resilience of Logic Locking Mechanisms using Formal Methods

Today, Integrated Circuits (ICs) manufactoring is distributed over various foundries, resulting in untrustworthy supply chains. Therefore, significant concerns about malicious intentions like intellectual property piracy of the fabricated ICs exist. Logic Locking (LL) is one well-known protection technique to improve the security of ICs. However, there are approaches to unlocking the circuit, like the SAT-based attack. Significant research has been done on thwarting the SAT-based attack by providing SAT-resilient LL. Nevertheless, these SAT-resilient LL approaches have an inherent structural footprint, yielding a high vulnerability to structural attacks. Recently, Polymorphic Logic Gates (PLGs) have been utilized to implement logic obfuscation by replacing gates. Reconfigurable Field Effect Transistors (RFETs) are a new emerging technology for implementing such PLGs due to their inherent camouflaging properties. This work proposes a novel technique for increasing SAT-resilience while introducing no structural weakness using those PLGs. In particular, based on the concept of an SAT-based attack, a procedure for determining the most SAT-resilient placement of LL-cells is developed. The experimental evaluation proves that the proposed hardening of the placement increases the SAT-resilience compared to a random placement while providing inherent camouflaging of RFET-cells.